The present invention relates to a method and a device for determining proportions of solid matter in a test material.
One example of a situation in which it is desirable to determine proportions of solid matter in a test material is in the detection of foreign matter and foreign fibers in a textile formation. In this case the detection is usually carried out by optical means. For example, foreign matter and foreign fibers are detected by their reflection properties, which in the majority of known cases differ from the reflection properties of a pure textile formation. The textile formation to be tested is therefore illuminated with light. The light absorbed by the test material and/or the reflected light is then detected. Instantaneous or local deviations of the received quantity of light give an indication of the proportion of desirable and undesirable matter.
A disadvantage of known methods and devices of this kind lies in the failure to detect colorless, transparent or translucent matter such as, for example, polypropylene sheets, or matter of a color which is similar to that of the textile formation, such as cables or cords, which are used when packing raw textile materials such as cotton, etc. This results in parts of such polypropylene sheets, cables and cords being subsequently processed with the raw material, with the result that these are later enclosed in a yarn, for example.
It is possible to detect solid matter such as polypropylene parts when spun in a yarn. In this respect it is assumed that this matter or these polypropylene parts change the structure of the yarn and, for example, the hairiness in a section of the yarn in particular. This is detected when measuring the diameter, for example by a change in the mass of the yarn or in the hairiness due to polypropylene parts projecting from the yarn instead of hairs. Attempts have therefore been made in this case to detect foreign parts by measuring the diameter, the mass or the hairiness.
One disadvantage of this detection of proportions of solid matter or of foreign matter by measuring the diameter or the hairiness lies in the fact that much of the foreign matter is not detected. This is primarily due to the fact that it is not located at the surface of the test material. As a result, unfavorable proportions of solid matter and other foreign matter give rise to an end product which is weakened or contains defects. A product of this kind may also be the cause of difficulties during subsequent processing, so that a defect-free end product cannot be produced.
The present invention solves the object of providing a method and a device by means of which proportions of solid matter in a test material can be easily and reliably determined, even in the case of transparent matter or matter of a similar color as the test material.
This result is achieved by exposing the test material to an electric field and determining dielectric properties of the field with the test material. In order to determine the dielectric properties of the field, electrical measurable quantities are measured, from which at least two electrical quantities are determined and combined, resulting in a characteristic value which is independent of the mass of the test material. The characteristic value is compared with comparative values, and information on the proportion of solid matter or the change thereof in the test material is obtained from the comparison. The dielectric properties can be detected on the basis of a plurality of electrical quantities.
A first possibility lies, for example, in determining, as an electrical quantity, the change in capacitance caused by the test material or the relative permittivity ∈r in an electric alternating field of at least two frequencies from measurable quantities such as voltage, current, phase shift between voltage and current and any reference resistances, and forming therefrom a quotient as a characteristic value.
A second possibility lies, for example, in determining, as a characteristic value, electrical quantities such as the power factor cos xcfx86 of the change in capacitance caused by the test material from measurable quantities such as voltage, current, phase shift between voltage and current and any reference resistances.
The characteristic value determined from the electrical quantities by, for example, forming a quotient, remains constant as long as the proportion of solid matter in the test material remains constant. Should the proportion change, this fact is indicated by a corresponding change in the characteristic value. The absolute proportion of solid matter in the test material may also be determined by forming a relation from the constant characteristic value and from the changed characteristic value.
A device for performing this method consists of at least one precision capacitor, which is disposed in the region of the test material to create an electric field, a frequency generator connected to the capacitor to generate at least one frequency in the electric field, measuring elements connected to the frequency generator for electrical measurable quantities, and an evaluation circuit for forming the electrical quantities and the characteristic value and for comparing the characteristic value with predetermined values.
In order to be able to cancel out the basic capacitance of the capacitor without the test material, a reference capacitor, connected to the same or to an inverted signal source, may be provided. The frequency generators preferably form a bridge circuit with the precision capacitor and the reference capacitor.
The dielectric properties of a field are represented by at least one quantity from a group of electrical quantities comprising capacitance, relative permittivity, loss angle and power factor.
The advantages achieved by the invention lie in particular in the fact that it enables the most varied foreign matter, compositions or proportions of solid matter in a test material to be detected, irrespective of whether certain matter is visible, invisible or of a similar color to the test material or whether it occurs inside or at the surface. The means provided for carrying out the method are of a simple structure and allow it to be combined problem-free with other measuring devices which measure other parameters in pursuit of other objects.